I've been reviving a Teac A4010-S reel to reel lately and have had difficulty finding a correct schematic for it. In Teac's defense, they sold a quarter million of these (with good reason) and the design evolved. I believe there are no less than five variants that occurred between the mid 60s and early 70's that are quite different. I have found three schematic variants so far but I can't find mine. Really hats off to a company that will evolve a product even though it's selling well......but......
Can you keep the documents pertinent and dated with reference to production dates?
Geesh......I have spent hours chasing down a problem only to conclude my schematic is not representative.
I have concluded that the guy who drew it apparently only had a symbol for a PNP transistor and not one for an NPN, and furthermore, this did not stop him from incorrectly showing PNP everywhere!
This got me to thinking. This seems to be a repetitive theme for me when fixing audio, current pieces or vintage.
If I have a correct schematic/bom/layout, I can fix anything within a half hour and will have identified the exact component(s) that are bad. Unfortunately, multiply that time exponentially if I'm missing any of the three, especially a correct schematic!
I find the biggest challenge when troubleshooting to be identifying signal flow. Typically there many features in an integrated audio piece of gear and this results in confusing signal routes. For example, many units from the seventies (the apogee of audio quality IMO) will panel mount controls and wire down to the board rather than PCB mount the controls which I applaud for reliability reasons. However, this allows the designer to put them anywhere on a panel with no deference to the signal flow. You must agree when troubleshooting one must identify a point where the signal is good then the point where it goes bad. This can be challenging with a feature laden piece of gear. This is where, yet another document, a block diagram comes into play. My Marantz 2245 docs include this and it has been immensely beneficial to reducing fix it time.
So...my point?
Any of you DIY folks, do yourself and the community a favor and create good documents. Someone may have to service your gear some day in the future when you are lying horizontal terra ferma.
Can you keep the documents pertinent and dated with reference to production dates?
Geesh......I have spent hours chasing down a problem only to conclude my schematic is not representative.
I have concluded that the guy who drew it apparently only had a symbol for a PNP transistor and not one for an NPN, and furthermore, this did not stop him from incorrectly showing PNP everywhere!
This got me to thinking. This seems to be a repetitive theme for me when fixing audio, current pieces or vintage.
If I have a correct schematic/bom/layout, I can fix anything within a half hour and will have identified the exact component(s) that are bad. Unfortunately, multiply that time exponentially if I'm missing any of the three, especially a correct schematic!
I find the biggest challenge when troubleshooting to be identifying signal flow. Typically there many features in an integrated audio piece of gear and this results in confusing signal routes. For example, many units from the seventies (the apogee of audio quality IMO) will panel mount controls and wire down to the board rather than PCB mount the controls which I applaud for reliability reasons. However, this allows the designer to put them anywhere on a panel with no deference to the signal flow. You must agree when troubleshooting one must identify a point where the signal is good then the point where it goes bad. This can be challenging with a feature laden piece of gear. This is where, yet another document, a block diagram comes into play. My Marantz 2245 docs include this and it has been immensely beneficial to reducing fix it time.
So...my point?
Any of you DIY folks, do yourself and the community a favor and create good documents. Someone may have to service your gear some day in the future when you are lying horizontal terra ferma.
Never saw that with a major. What I have seen are potted internal modules that had to be ordered as complete units from the manufacturer as well as custom markings on ordinary parts.
An parts placement guide is of little use without an schematic, as far as troubleshooting is concenred.
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Update - I finally located the correct service manual. Turns out I have the Teac S-1040SL model which came out toward the end of the model life. It has tape bias type switches so one can play the newer 1/4" tape that had come out in the early 70s. I'd say the schematic in the manual is 99% correct which was very helpful. It's amazing how much the electronics changed design, even topology, over it's product life. I had a distorted right channel which turned out to be an NPN transistor pair that some how exhibited an out of spec gain. Really odd - I've never seen that before. Usually if you can measure a a transistor's base/collector and base/emitter forward drop using the diode scale on a volt meter then it's ok. Not this time! The bias point had drifted to the point the lower half of the waveform was severely compressed. I found a substitute transistor type in my mediocre collection, replaced them, and now the deck sounds great. Nonetheless, somebody shoot me if I ever design a single sided PCB with no reference designators! That was a b!@#$ to trouble shoot and repair. I lifted a couple pads by mistake in fact.
In 80's YAMAHA used to pot their Motorcycle Ignition and control electronics with an epoxy slurry FULL of broken Glass shards.. (Can't begin to make this level of Stupidity up)
All that to protect their market leading (in their wee minds) 8 bit technology
I feel guilty now for bashing Teac. My player is a such late model S-410SL that it more closely resembles the S-410GSL. The G stands for glass heads. There are no other differences I have observed. The service manual for the GSL is spot on with accurate schematics and has a great deal of calibration/adjustment info. It has several block diagrams in fact. Tx Teac!
Lesson learned - take the time to get a pertinent manual.
Lesson learned - take the time to get a pertinent manual.
This post from tubelab, describes the problem, it's initially about cars, but he mentions it also being a problem with electronics. The car thread
Tony.
Tony.
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